Schiff base developing agent precursors



Sept. 1967 R. L. REEVES 3,342,599

SCHIFF BASE DEVELOPING AGENT PRECURSORS Filed June 7, 1965 BLUE SENSITIVE SILVER HAL/OE l6 CON TA IN/N G YE L LOW COUPL ER CL 5 LAYER GREEN SENSITIVE SILVER HAL/OE /4 CONTAINING MAGENTA COUPLER /3 ELAT/N INTER LAYER RED SENSITIVE SILVER HAL/05 CONTAINING CYAN COUPLER DEVELOPING AGENT PRECURSOR AND ANTIHALAT/ON LAYER /0 suppom RICHARD L. REEVES INVENTOR.

m WM A T TORNEYS United States Patent 3,342,599 SCHIFF BASE DEVELOPING AGENT PRECURSORS Richard L. Reeves, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed June 7, 1965, Ser. No. 461,698

17 Claims. (Cl. 9666.2)

This invention relates to photographic compositions in which developing agents are incorporated in an inert precursor form. In particular, this invention relates to new storage-stable, alkaline-activatable, developing agent precursors for use with such products.

Photographic developing agents are active reducing chemicals and generally suffer from instability when used in aqueous processing baths or when incorporated into photographic layers which must have a reasonable storage life. However, it is often desirable to incorporate them alone or with other processing addenda, in the photosensitive material and it is important to be able to do so without modifying the sensitometric characteristics adversely.

To obviate this problem it has been proposed to use a stable, inert precursor compound which can be decomposed to generate the desired developing agents rapidly when needed, for example, by treatment with an alkaline activating solution. The prior art compounds disclosed are often inadequate for practical applications, either showing inferior keeping qualities in the photographic material or releasing the active developing agent too slowly in processing.

One object of my invention is to provide new and improved developing agent precursors which can be incorporated in stable form in photographic materials and can be rapidly cleaved by alkaline treatment to yield active developing agents.

Another object of my invention is to provide new and improved color-developing agent precursors which can be incorporated in stable form in photographic layers and can be rapidly cleaved by alkaline-treatment to yield active color-developing agents.

A further object is to provide new and improved developing agent precursors which are photographically compatible when incorporated into a silver halide emulsion or adjacent layers.

Another object is to provide new and improved developing agent precursors (including color-developing agent precursors) which are more rapidly soluble in aqueous liquids than the parent developing agent.

A further object of my invention is to provide new and improved developing agent precursors which have a high resistance to oxidation in solution or in photographic layers, and which resist hydrolysis in aqueous medium at moderate pHs up to about pH 9, but hydrolyze very rapidly to yield active developing agents at higher pHs.

A still further object is to provide color photographic layers which can be color developed by immersing in an alkaline activator solution.

Another object is to provide such developing agent precursors having ballast groups which decrease the diffusibility of the precursor compound.

Still another object is to provide developing agents in a precursor form showing reduced allergenic and toxic propensities.

Still another object of my invention is to provide new and improved multilayer color photographic materials in which the emulsion layers are provided with appropriate color-developing agent precursors, of this invention, the concentration and chemical structure of the agents being selected to fit the individual requirements of the different emulsion development.

Still another object is to provide multilayer photographic elements containing my new and improved developing agent precursors in any or all layers of said element. Other objects will be apparent from the following disclosure.

The objects of my invention are achieved by using as development precursors compounds prepared by reacting the primary amino functional group or groups of a silver halide developing agent with a salicylaldehyde to form Schiffs bases which resist hydrolysis at pHs below about 9, and which hydrolyze rapidly at pHs over 9 to yield active amino developing agents.

The developing agent precursors of my invention made by using known aromatic amine developing agents can be represented by the following general formula:

wherein R represents -OH,

in which R may represent alkyl having from 1 to 18 carbon atoms, and R represents hydrogen or alkyl having from 1 to 12 carbon atoms. These alkyl groups may contain substituent groups such as hydroxyl, carboxyl, sulfo, alkoxy, carboalkoxy, carboaryloxy, sulfoalkoxy, sulfoaryloXy, and an amide group, e.g., acetamido, N-methylcarbamyl, methylsulfonamido, N-methylsulfamyl, sulfamyl, etc. R and R may also represent the non-metallic atoms necessary to complete a 5- or 6-membered heterocyclic ring. R and R may also represent the non-metallic atoms necessary to complete a 5- or 6-membered heterocyclic ring. R may also represent I N=CH -R4 (5H 1' in which R R and R each represent hydrogen,

R and R above. R R R and R each. represents hydrogen,

as defined above, alkoxy, alkyl (each of these two groups may contain from 1 to 18 carbon atoms and may also contain substituent groups as defined for R and R above), and halogen. R may also represent I I OH R R and R may also represent the non-metallic atoms necessary to form a 5- or 6-membered isocyclic or heterocyclic ring. R and R may also represent the non-metallic atoms necessary to complete a 5- or 6-Inembered isocyclic or heterocyclic ring.

The starting compounds, i.e., developing agents and salicylaldehydes used to form the precursors, may contain substituent groups to modify such characteristics as development reactivity, solubility, diffusibility, etc. They may also contain other substituents, such as, for example, ultraviolet absorbers, antistain agents, stabilizing agents, couplers, dyes, etc.

Color developing agent precursor compounds typical of those of this invention are illustrated, for example, by the following:

(1) N ethyl-N-(B-hydroxyethyl)-4-salicylideneaminoaniline (2) N ethyl-N-(,B-sulfoethyl)-3-rnethyl-4-salicylideneaminoaniline (3) N ethyl-N-(fi-hydroxyethyl)-4-{5-[5-(3,5-disulfobenzamido) 2 (2,4-di-t-arnylphenoxy)benzamido]salicylideneamino}aniline disodium salt CzHs C2H4OH l NaOgS- SO Na l Cs n-t (4) 4-salicylideneaminophenol (6) 'N ethyl N methyl 3 (di ,6 hydroxyethylamino) -4-(5-octylsulfonamidosalicylideneamino) aniline Cs u (7) N dodecyl N ethyl 4 (5 sulfosalicylideneamino)ani1ine sodium salt (8) 4 (4 octadecyloxysalicylideneamino) 2 methylphenol (9) N ethyl N "(,8 hydroxyethyl) 4 (4 octadecyloxysalicylideneamino)aniline [10) 1 1,N diethyl 4 (5 aniline sodium salt sulfosalicylideneamino) In one form of my invention my novel developing agent precursors are incorporated in light-sensitive photographic compositions, e.g., silver halide emulsions, or associated layers used in black-and-white and in color photography. Advantageously my novel precursor compounds are located in a light-sensitive or light-insensitive layer or proportioned between two or more such layers. These compounds undergo rapid cleavage to the respective developing agent and salicylaldehyde in the presence of an alkaline solution at pHs above about pH 9. p

In another advantageous form of the invention the precursor compounds are incorporated in layers separate from the photosensitive compositions; such layers include processing webs containing processing materials which are brought into contact with the exposed photographic element to effect latent image development. Special forms of webs containing these precursors also provide nuclei or other metal-precipitating agents for the formation of diffusion transfer metal images. Other forms comprise, in addition to the precursor compounds, mordants or other means for fixing diffusion transfer dye images.

In another form of my invention diifusible precursors are used to advantage in dry powder or liquid compositions for the preparation of alkaline developer solutions, in which they hydrolyze rapidly to the active developer, to develop light-sensitive photographic elements. Compounds 1, 2, 4 and 10 are particularly useful in solutions to color develop photographic elements which contain incorporated couplers or those utilizing developer solutions containing difiusible couplers. In some instances, the precursor is more soluble than the developing agent from which it was prepared, and this can be invaluable in facilitating the preparation of developer solutions from dry powder compositions, particularly when solubilizing groups are not wanted on the developer because of requirements in the formation of nondiftusible image dyes.

The precursor compounds of my invention are also advantageous in solid or liquid compositions for preparing photographic developing solutions which are stable to oxidation and may be stored for long periods. Such compositions preferably contain no highly alkaline material, the alkali or alkaline butler being added immediately before development, thus releasing the active developing agent.

The following table gives useful amounts of the various ingredients which may be used in making up solutions or powders containing the precursor compounds of this invention. However, other amounts may be used depending upon the emulsion, desired result, use of auxiliary developers, etc.

Developing agent precursor g 1-20 Diifusible coupler (competing or image-forming) g 0-10 Alkaline salt g 0-100 Alkali metal sulfite g 0-50 Alkali metal bromide 'g 01() Hypo g =0-20 Thickening agents g 040' Water liter 0-1 My developing agent precursor compounds may be used either alone or in a combination of two or more such compounds. They may also be used in combination with other developing agents such as p-phenylenediamines, p-aminophenols, hydroquinones, aminopyrazolones, aminopyrazolines, pyrazolidones, etc.

Color developing agents which can be used in preparing precursor compounds useful in my invention include such compounds as, for example, diethyl-p-phenylenediamine hydrochloride, monomethyl-p-phenylenediamine hydrochloride, dimethyl-p-phenylenediamine hydrochlon'de, Z-amino-5-diethy1aminotoluene hydrochloride, 2- amin 0-5 N-ethyl-Ndaurylamino) toluene, N-ethyl-N- (/3- methanesulfonamidoethyl)-3-methyl 4-aminoaniline sulfate, N-ethyl-N-(,B-rnethanesulfonamidoethyl) 4-aminoaniline, 4-[N-ethyl-N 3 hydroxyethyl)amino] aniline, etc., the 4-aminophenols, e.g., Z-chloro; 2,6-dibromo; 2,6- diiodo; 3-methyl 2,6-dimethyl, and 2-ethyl 4-aminophenols; 4-aminopyrazolones, 3-aminopyrazolines, etc. Other conventional developing agents may also be used including, for example, p-phenylenediamines, o-phenylene diamines, o-aminophenols, paminophenols, o-diaminophenols, p-diaminophenols, 4-aminopyrazolones, 3-aminopyrazolines, etc.

When my compounds are incorporated in emulsion layers or adjacent layers, they are particularly useful in the range of from about 0.5 to about 25 moles of precursor per mole of silver halide. Concentrations beyond these limits are also useful in other circumstances depending upon the emulsion, etc.

The nondilfusing precursors of my invention are used to advantage in photographic emulsion layers or adjacent layers. Compounds 3 and 7 are particularly useful incorporated by the Fischer method, such as that as applied to dye-forming couplers described in US. Patent 2,186,849, and as applied to ultra-violet absorbers as 7 described in U.S. Patents 2,685,512; 2,719,086; 2,739,888; and 2,784,087.

Nonditfusing compounds 5, 6, and 9 can be incorporated in emulsion layers by (1) solvent dispersion techniques such as are described for oil soluble couplers in U.S. Patent 2,304,939, (2) or using high-boiling organic solvents as set out in U.S. Patent 2,322,027 and (3) by methods described in US. Patent 2,801,170, and U.S. Patent 2,801,171, and U.S. Patent 2,949,360, in which low-boiling or water-soluble organic solvents are used with or in place of the high-boiling solvent. The use of such precursor dispersions permits thinner layers, which are very desirable, because they cause less light scattering, consequently, they produce sharper images.

My precursors are used in the color development of photographic hydrophilic colloid-silver halide emulsion layers of the developing-out type either in the color developer solution or in the emulsion layer. The emulsions may contain silver chloride, silver bromide, silver iodide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, etc., as the light-sensitive material.

The precursors of my invention may also be used to advantage in image-forming layers with image-forming metal salts other than silver halide, such as ZnO, ZnS, CdS, CdSe, NiS, etc., in binders such as gelatin, polyvinyl alcohol, etc.

i Hydrophilic colloids used to advantage include gelatin, colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate.

The emulsions used in the photographic element of my invention can be chemically or optically sensitized. These emulsions can be coated on a wide variety of photographic emulsion supports.

Color photographic materials embodying these precursors typically comprise a photographic support coated in succession with a red-sensitive layer, a green-sensitive layer, and a blue-sensitive layer either with or without a Carey Lea filter layer between the blue-sensitive and green-sensitive layers. The three differentially color sensitized layers may be arranged in other orders. Couplers may be incorporated in the layers and the dyes formed may be insoluble or may be diffused and mordanted or fixed in reception layers, which may be separate or may be an integral part of the light-sensitive element. The reception layer comprises a hydrophilic colloid layer containing a cationic mordant, e.g., the polymers of amino guanidine derivatives of vinyl methyl ketone such as described in Minsk U.S. Patent 2,882,156. Other mordants include the 2-vinyl pyridine polymer quaternized with methyl-p-toluene sulfonate and similar compounds.

In general, the developing agent precursor compounds of my invention are prepared by stirring a warm mixture of a developing agent and a salicylaldehyde or substituted salicylaldehyde and concentrating the resulting solution until the product is precipitated. A typical synthesis is described in Example 1 below.

A typical negative color process which can be used in our invention is described in detail by W. T. Hansen, .lr., and W. I. Kisner in an article in the Journal of the Society of Motion Picture and Television Engineers, vol. 61 (1953), pages 667-701, incorporated herein by reference.

Example 16 of U.S. Patent 2,944,900, also incorporated herein by reference, discloses a reversal color development process which can be used in my invention.

The attached drawing illustrates a multilayer color photographic element. A cellulose acetate opaque white film support has in order, beginning with the support, a gelatin layer 11 containing the developing agent precursor which also serves as the antihalation material. Over the precursor layer is coated a gelatino-silver bromoiodide emulsion 12 sensitized to red light, a gelatin interlayer Example 1 Preparation of N-ethyl-N-(B-sulfoethyl) 3 methyl-4- salicylideneaminoaniline, Compound N0. 2.A slurry of 12.9 g. of N-ethyl-N-B-sulfoethyl-B-methyl-4-aminoaniline in deaerated water and a solution of 6.1 g. of salicylaldehyde in deaerated methanol were poured together and stirred wtih warming until a homogeneous solution resulted. The solution was concentrated until the product precipitated. The product was recrystallized from methyl alcohol-water mixtures by slowly evaporating the solvent. The melting point was 177179 C. with decomposition.

Example 2 The compounds of my invention are particularly advantageous because of the rapidity with which the developing agent is released on hydrolysis of the developing agent precursor in alkaline solutions of high pH, such as pH 12; a property which is not exhibited by color developing agent precursors in the prior art. For example, Compound No. 2 of Example 1 releases the developing agent approximately 1600 times faster at pH 12 than does the prior art compound, N,N-diethyl- 3 methyl 4 (2-sulfobenzylidene amino)aniline sodium salt.

Example 3 A weighed sample of developing agent precursor sufficient to give a 1 10- M solution after dilution, is dissolved in 1 ml. of ethanol in a volumetric flask and thermostated at 25.0 C. This sample is diluted to ml. with aqueous phosphate or carbonate butter having an ionic strength of 0.05. The disappearance of the developing agent precursor is followed on a Beckman DU spectrophotometer at a wavelength that gives the greatest difference in absorbance between the precursor and aldehyde. The first-order rate constants are calculated by the Guggenheim method.

The following example illustrates the ability of the compounds of my invention to release active developing agent during the processing of a photographic element.

Example 4 A single layer gelatin-silver bromoiodide emulsion was coated on a conventional support. The constituents per square foot of coated emulsion comprised: 7.8 parts of gelatin, 3,3 parts of silver, 1 part of the coupler, l-phenyl- 3-(3,5-disulfobenzamido) 4 (2-hydroxy-4-pentadecylphenylazo-)-5-pyrazolone dipotassium salt, and 1.7 parts of Compound No. 3 as the developing agent precursor.

A second single layer control coating was prepared that was similar in all respects to the first coating except that a non-salicylidene developing agent precursor was used: N-ethyl-N- (B-hydroxyethyl)-4-{5-[S-(3,5-disulfobenzamido)-2-(2,4 di t amylphenoxy)benzamido] benzylidene}aniline.

Samples of the above mentioned coatings were exposed (i.e., /2-second exposure through a 0.3 neutral density step tablet) and processed as follows:

The exposed film strips were dipped for 35 seconds in an activator solution having the following composition:

Na CO monohydrate g 20 Ascorbic acid g 0.2 Water to pH to 11:0 liter 1 The strips were then developed for 5 minutes at 75 F. in contact with a previously soaked mordant receiving sheet (i.e., which had been soaked for 25 seconds in the same activator solution). The strips were then separated and mordanted receiving sheets containing the transferred magenta dye images were washed for minutes in water and dried. The magenta dye density (i.e., to green light) in the D max. region of the strip from the first coating was 1.22. That of the strip from the second coating (control) was 0.50. This difference in density is due to the difference in hydrolysis rates between the two developing agent precursors.

Example 5 A storage-stable processing web was prepared by applying a gelatin coating containing 5 parts by weight of gelatin and 1 part by weight of Compound No. 3 (suflicient to yield enough active developing agent to completely develop the multilayer color film described below) onto a subbed cellulose acetate support.

An exposed sample of a multilayer color film similar to that described in Example 16, part 1, of Carroll, Elins, Graham, and Wilson US. Patent 2,944,900, issued July 12, 1960, was color developed by immersing the film sample first for 15 seconds in an alkaline activator solution (5 g. sodium hydroxide; g. sodium carbonate monohydrate; 10 g. sodium sulfite desiccated; and water to 1 liter), then bringing the emulsion side of the wet film into firm contact with the gel side of a sample of the above described processing web containing Compound No. 3 which had also been presoaked for seconds in the alkaline activator solution. After 10 minutes, the color film was separated from the gel pad, bleached (i.e., in a ferricyanide bleach), fixed in Kodak F-S fixing bath, washed in Water, and dried.

A good quality negative color reproduction of the subject was obtained.

Example 6 A multilayer color film similar to that described in Example 5 was prepared except that it was coated over a gelatin layer (i.e., which had been coated on a clear cellulose acetate film support) which contained a sufiicient amount of precursor Compound No. 10 to yield enough active developing agent to completely develop the color film.

An exposed sample of this film was developed by wetting with the alkaline activator solution of Example 5 and permitting the development to proceed in the wet film for a period of 10 minutes, after which time the film was bleached (i.e., in a ferricyanide bleach), fixed in Kodak 1 F-5 Fixing Bath, washed in water, and dried.

The processed film contained a good quality negative color reproduction of the subject.

The practice of my invention comprises the use of N-salicylidene derivatives of developing agents containing at least one amino group as inert precursors of the developing agents. These derivatives cleave readily under alkaline conditions to yield the active form of developing agent.

Although the composition of the moiety to which the amino group is attached has no effect on the inertness of the precursor compounds of my invention and their rapid decomposition under alkaline conditions, it will be understood that changes in the character and degree of substitution of said moiety can be made to satisfy specific requirements of reactivity, solubility, and diffusibility imposed when my compounds are incorporated in photographic compositions.

My novel compounds are used to advantage in developing photographic film (i.e., either black-and-white or color film) containing magenta couplers, e.g., pyrazolones,

1 See the following table Kodak F5 Fixing Bath g Water to make 1 liter.

cyanoacetylcoumarones, indazolones, etc., yellow couplers, e.g., a-acylacetanilides, dibenzoylmethanes, etc., and cyan couplers, e.g., naphthols, phenols, etc., which couplers can form either diffusible or n-onditfusible image dyes.

They are also used to advantage with developer solutions which contain ditfusible couplers, which couplers form nondiffusible image dyes in the film. They provide, on color development, the same dyestufl? with the above mentioned couplers as does the parent coupler since the aldehyde is split off by the alkali of the developer solution.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected Within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claims:

1. In a dry silver halide developing composition adapted to be mixed with water for developing a latent image in a silver halide emulsion the improvement comprising, as a developing agent precursor, a Schiif base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydrolyzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide developing agent.

2. In an aqueous silver halide developing concenerate the improvement comprising, as a developing agent precursor, a Schiff base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydrolyzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide developing agent.

3. A light-sensitive unexposed silver halide emulsion containing therein, as a developing agent precursor compound, a Schiif base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydroylzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide developing agent.

4. A photographic element comprising a support having thereon a light-sensitive unexposed silver halide emulsion containing therein, as a developing agent precursor, a Schifi. base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydrolyzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide developing agent.

5. A light-sensitive photographic element comprising a support having thereon a coating containing, as a developing agent precursor, a Schiif base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylidene amino group and having the property of hydrolyzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide developing agent.

6. A photographic element comprising a support having thereon an unexposed light-sensitive silver halide emulsion containing N ethyl N-(B-hydroxyethyl)-4- salicylideneaminoaniline.

7. A photographic element comprising a. support having thereon an unexposed light-sensitive silver halide emulsion containing N-ethyl-N-(fl-sulfoethyl)-3-methy1-4- salicylideneaminoaniline.

8. A photographic element comprising a support having thereon an unexposed light-sensitive silver halide emulsion containing N-ethyl-N- (fl-hydroxyethyl)-4-{5-[5- (3,5 disulfobenzamid-o) 2(2,4-di-t-amylpi1enoxy) benzamido]salicylideneamino}aniline disodium salt.

ill

9. A photographic element comprising a support having thereon an unexposed light-sensitive silver halide emulsion containing 4-salicylideneaminophenol.

10. A photographic element comprising a support having thereon an unexposed light-sensitive silver halide emulsion containing N-ethyl-N-(B-methylsulfonamidothyl) 4 {4-[a-(3 pen-tadecylphenoxy)acetamindo] salicylideneamino}aniline.

11. A light-sensitive element as in claim 5 wherein said coating also contains a mordant for dyes.

12. A photographic element comprising a support having thereon an unexposed light-sensitive silver halide emulsion layer containing at least one color former which reacts with the oxidation product of a primary aromatic amine color developer and having asa developing agent precursor, a Schiff base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydrolyzing rapidly at a pH above 9 to release a primary amino siliver halide color development agent.

13. A photographic element as in claim 12 wherein said developing agent precursor is contained in an alkali permeable layer contiguous to said emulsion layer.

14. A light-insensitive photographic element comprising a support having thereon a coating containing silver halide precipitating nuclei and, as a developing agent precursor, a Schiif base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydrolyzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide developing agent.

15. A rnulti-layer photographic element comprising a support having thereon at least one layer containing an unexposed light-sensitive silver halide emulsion containing at least one color coupler which reacts with the oxidation product of a primary aromatic amine color developer to form a dye and containing in at least one layer, as a developing agent precursor, a Schiff base which is a condensate of a salicylaldehyde with a silver halide developing agent, said condensate having at least one salicylaldehyde amino group and having the property of hydrolyzing rapidly at a pH above 9 to release said primary amino silver halide color developing agent.

16. A multi-layer photographic element comprising a support with thereon at least one unexposed photographic silver halide emulsion layer sensitive to the blue region of the spectrum, at least one layer spectrally sensitized to the green region of the spectrum, and at least .one unexposed photographic silver halide emulsion layer spectrally sensitized to the red region of the spectrum, and containing in at least one layer of said multi-layer photographic element, as a developing agent precursor, a S-chiff base which is a condensate of a salicyladehyde with a silver halide developing agent, said condensate having at least one salicylideneamino group and having the property of hydrolyzing rapidly in alkaline medium at a pH above 9 to release a primary amino silver halide color development agent.

17. In a process of developing an exposed silver halide emulsion containing a developing agent precursor the improvements comprising (a) employing, as said developing agent precursor, a Schiff base which is a condensate of a salicylaldehyde with a siliver halide developing agent, said condensate having at least one salicylideneamino group and (b) contacting said emulsion with an alkaline agent to raise the pH of said emulsion to above 9 and to release said silver halide developing agent from said precursor.

References Cited UNITED STATES PATENTS 2,507,114 5/1950 McQueen 96-66.4 2,695,234 11/1964 Iaeken et al. 96-66.4 3,132,140 5/1964 llafiie 260240 NORMAN G. TORCHIN, Primary Examiner.

C. E. DAVIS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,342,599 September 19, 1967 Richard L. Reeves It is hereby certified that error appears in the above numbered pat.- ent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, lines 58 to 75, for that portion of the formula reading -C H "t read -C5H 1-t column 5, 'lines 39 to 52, for that portion of the formula reading [2 4 read 2 5 column 7, line 3, after "6," insert 8 line 6, after "or" insert by column 8, lines 1 and 2, for "sensitizer" read sensitized column 10 line 18, for "claims" read claim column ll, line 7, for "thy1) 4-{4 [on-" read ethyl)-4-{4-[a- Signed and sealed this 29th day of October 1968.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A DRY SILVER HALIDE DEVELOPING COMPOSITION ADAPTED TO BE MIXED WITH WATER FOR DEVELOPING A LATENT IMAGE IN A SILVER HALIDE EMULSION THE IMPROVEMENT COMPRISING, AS A DEVELOPING AGENT PRECURSOR, A SCHIFF BASE WHICH IS A CONDENSATE OF A SALICYLALDEHYDE WITH A SILVER HALIDE DEVELOPING AGENT, SAID CONDENSATE HAVING AT LEAST ONE SALICYLIDENEAMINO GROUP AND HAVING THE PROPERTY OF HYDROLYZING RAPIDLY IN ALKALINE MEDIUM AT A PH ABOVE 9 TO RELEASE A PRIMARY AMINO SILVER HALIDE DEVELOPING AGENT. 